In the opening of George Orwell's Animal Farm, the Old Major gives a speech in which he discusses the "state" of England. He presents the audience with a set of questions: "What is the nature of this life of ours?" and "Is it simply part of the order of nature?" To answer the first question, the Major expresses how the animals in England work their fingers to the bone and produce enough to sustain a large number of animals (a dozen horses, twenty cows, and hundreds of sheep), but they have nothing to show for it. With this, the Major attributes all of the problems of English society to the very presence of the "Corporate Communist Elite," who take everything the animals produce.
As an answer to the second, the Major emphatically asserts that this order is hardly natural. The land of England is not so poor as to require the "Corporate Communist Elite" to maintain it. His intention is to rouse the animals of England to rebel against their oppressive system of government.
The Major insists the animals sing "Beasts of England" to allow them to look forward to the time, whether it is a day, a week or a hundred years, when they will be free of the communist yoke. In the song, the Major's lyrics instill in the animals the desire to work toward that goal. In doing so, it essentially becomes a rallying cry for them.